Surface wave transducer for digital signals

ABSTRACT

Surface wave transducers of the interdigital type for generating and detecting return to zero pulse sequences of surface waves are disclosed. The transducer, which is located on the surface of a suitable surface wave medium, is an interdigitated electrode array including main electrodes that are perpendicular to the transducer leads and auxiliary electrodes that are inclined at an angle to the main electrodes.

I United States Patent 1151 3,680,007 Tseng 1 July 25, 1972 54] SURFACE WAVE TRANSDUCER FOR 3,568,102 3/1971 Tseng ..333/30 DIGITAL SIGNALS 3,376,572 4/1968 Mayo .343/17.2 3,559,115 1/1971 De Vries... ....333/72 [721 chmchmg Tan! 3,573,673 4/1971 De Vries ..333/72 [73] Assignee: International Business Machines Corpora- 3,548,306 12/1970 Whitehouse ..324/80 tion, Armonk, NY.

Primary Examiner-Eli Lieberman [22] Flled' 1970 A!rmeyHanifin and Jancin and John J. Goodwin [211 App]. No.: 76,942

[57] ABSTRACT [52] US. Cl. ..333/30 R, 3 l0/9.8 S f wave transducers f the i t di iufl type for generab [51] Int. Cl. ..H03h 7/30 ing and detecting return m zero pulse sequences of surface Fidd Search "333/701 30 R; 310/82 waves are disclosed. The transducer, which is located on the 343/17'2 surface ofa suitable surface wave medium, is an interdigitated electrode array including main electrodes that are perpen- [56] Reterences cued dicular to the transducer leads and auxiliary electrodes that UNITED STATES PATENTS are inclined at an angle to the main electrodes.

3,551,837 12/1970 Speiser et a1 333/ 8 Claims, 6 Drawing Figures 3 4 [48 ,aa .4. 6B

IL -44 4O 64 I 94 P'lXTENTEl'lJuLzs m2 SHEET 2 BF 2 FIG45 FIG.6

SURFACE WAVE TRANSDUCER FOR DIGITAL SIGNALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is in the field of surface wave electronics, and, more particularly, relates to an interdigital transducer for surface wave generation and detection.

2. Prior Art An interdigital transducer for detecting digital surface wave signals is discussed in the publication Linear Signal Processing and Ultrasonic Transversal Filters," William D. Squire et a1, IEEE Transactions on Microwave Theory and Techniques, Volume MTT-l7, No. l 1, Nov. 1969, pages 1020-1040. FIG. 12 of the article shows the prior art transducer which differs from the present invention in that it employs only perpendicular electrodes and does not generate and detect return to zero pulse sequences. Furthermore, in the three electrode transducer described in the prior art, the center finger takes the entire load current of the device, and is very easily overloaded.

7 SUMMARY OF THE INVENTION An object of the present invention is to provide a transducer for generating and detecting surface waves.

Another object of the present invention is to provide a transducer for generating and detecting return to zero binary sequences of surface waves.

A further object of the present invention is to provide an interdigitated surface wave transducer having auxiliary electrodes.

The foregoing and other objects features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.

Surface waves are elastic waves which are propagated predominantly on the free surface of a solid. Surface wave electronics are significant since the surface waves are accessible along their entire length and are compatible with integrated circuit technology. Surface waves can be channeled, sensed, focused, mixed, amplified and otherwise employed in signal processing.

One way of generating and detecting surface waves is by depositing an interdigitated electrode array or grid structure on the surface of a piezoelectric substrate. An example of this structure is shown in U. S. Pat. No. 3,376,572, which issued on Apr. 2, 1968 to R. F. Mayo and entitled Electroacoustic Wave Shaping Device. The interdigital transducer includes a lead having a plurality of electrodes, also referred to as fingers, extending perpendicularly from the lead. The characteristics of the generated surface wave depend on the number of fingers and their spacing. The conventional interdigital surface wave transducer, with more than two fingers, can be used to process radio frequency pulses but not video pulses. This is because the transducer itself is a band-pass filter with finite bandwidth about a resonance frequency, and the bandwidth is inversely proportional to the number of fingers.

ln order to increase the gain bandwidth product of transducers for the video pulses used in data processing, coding theory has been used such as the Barker Code and the Golay Code. In the simplest Golay Code, which will be used as an example, surface wave pulse train is represented by two digit complementary sequences (+1, +1) and (+1, 1). The autocorrelation functions of these sequences are, respectively (+1, +2, +1) and (l, +2, 1 The sum of the two autocorrelation functions is the output sequence (0, +4, The advantage of this type of coding is seen from the fact that the complementary sequence input signals have digits with one unit of amplitude, while the output signal has a digit with four units of amplitude at the center and zero elsewhere. Thus, the output has a four-times-better signal to noise ratio than the input acoustic wave pulse train.

Referring to FIG. 1, two transducers 10 and 12 are located on substrate 14 having the two complementary surface wave pulse sequences 16 and 18 propagated thereon. Pulse sequence 161s the (+1, +1) and sequence 18 is the (+1, I When sequence 16 reaches transducer 10, the transducer performs the autocorrelation function to produce the (+1, +2, +1) sequence 20. Likewise, transducer 12 receives sequence 18 and autocorrelates to produce the (-l, +2, --1 sequence 22. When the outputs from transducers l0 and 12 are summed, the sequence (0, +4, 0) results, which is the single pulse 24. In this instance, the transducers function as detectors of the return-to-zero sequences 16 and 18;

ln FIG. 2, another pair of transducers 26 and 28 are added to the structure of FIG. 1 to function as generators of the complementary sequences. Transducers 26 and 28 receive the video pulse 30 as an input and generate sequences 16 and 18.

1t is to be noted that the code sequences are in return-tozero form, which is the manner in which the code is meant to be used. In prior art systems using transducers having all the fingers perpendicular to the lead, the first code sequence is generated as a sequence of two sine waves, which has a polarity of (+1, l, +1, I); and the first and third elements are used to represent the sequence. The second sequence is represented by a sine wave and a cosine wave, which has a polarity (+1, 1 l +1 and the first and third elements are used to represent the sequence. Such prior art systems have the disadvantage that the transducer generators must be connected to a balanced source, and the transducer detectors must be connected to a balanced load to assure complete cancellation at the output.

Referring to FIG. 3, an embodiment of the structure of an interdigital transducer for generating and detecting the returnto-zero surface wave signals is shown.

The first generating transducer 32 on substrate 11, which may be composed of piezoelectric material, includes a lead 34, a pair of main electrodes 36 and 38, a lead 40 and a pair of main electrodes 42 and 44. A first auxiliary electrode 46 is connected at an angle to main electrode 42, and a second auxiliary electrode 48 is connected at an angle to main electrode 38 such that auxiliary electrodes 46 and 48 are parallel. Although the auxiliary electrodes are shown connected to main electrodes, they need not be connected and may just be located in the region between the two leads. Referring to FIG. 4, the pulse sequence produced by transducer 32 is depicted. If there were no auxiliary electrodes, the positive pulses would be produced by the finger pairs 36 and 42 and 38 and 44. The negative pulse depicted by the dotted line would be produced by electrode pair 38 and 42. However, due to the presence of auxiliary electrodes 46 and 48 and the fact that they are at an angle, the dotted line negative pulse is not present; and, instead, a pulse is produced by the auxiliary electrode pair 46 and 48, which propagates ofi" in a different direction from the position pulses thereby achieving the (+1, +1) sequence. The pulse generated by the auxiliary electrodes 46 and 48 will propagate in a direction perpendicular to the electrodes, and will not be intercepted by receiving transducer 64.

Referring again to FIG. 3, the other generating transducer operates in a similar manner except that electrode pair 50 and 52 produce a positive pulse, and electrode pair 54 and 56 produce a negative pulse. Main electrodes 52 and 54 are connected to the same lead and should be at the same potential and will, therefore, not produce a pulse. Theoretically, then auxiliary electrodes 58 and 60 are not required. In practice, although the main electrodes 52 and 54 are at the same potential, the electric field between the electrodes 52 and 54 may not be zero (the line integral of the field from 52 to 54 is zero) and may produce a small pulse, which will be positive or negative depending on whether electrode 52 is positive or negative with respect to electrode 54. To prevent such occurrence, auxiliary electrodes 58 and 60 are included to propagate the small pulses in a different direction.

The preceding description indicated how the two transducers generate the (+1, +1) and to (+1, 1) sequence. The (+1, +1) sequence is detected by transducer 62 to produce a (+1, +2, +1 sequence, and the (+1, l) sequence is detected by transducer 78 to produce a (l, +2, 1) sequence as illustrated in FIG. 2. In FIG. 3, the first positive pulse hits electrode 64, which produces a positive pulse (+1) on the upper lead 64 when the first surface wave pulse is between main electrodes 64 and 66. When the first positive surface wave pulse reaches the region between electrodes 68 and 70, it again produces a positive pulse on lead 65. However, at the same time, the second positive surface wave pulse of the sequence has reached electrode 64 and also produces a positive pulse on lead 65. The two simultaneous positive pulses add together (+2). Finally, the second positive pulse of the sequence reaches electrode 68 to produce a positive pulse on lead 65 (+1). The total output sequence on lead 65 is therefore (+l,+2,+l).

Referring to transducer 78, the first negative pulse reaches electrode 80 to produce a negative pulse on lead 81 1). When the negative pulse reaches electrode 86, it makes electrode 86 negative with respect to lead 88, which produces a positive pulse on lead 81. At the same time, the second pulse of the sequence, which is positive, reaches lead 80 and also produces a positive pulse on lead 81. The two positive pulses add together (+2). Finally, the second (positive) pulse of the sequence reaches electrode 86. Electrode 86 becomes positive relative to electrode 88, which produces a negative pulse on lead 81 (l). The total output sequence on lead 81 is therefore (l, +2, 1 Leads 65 and 81 are connected together, and the two output sequences (+1, +2, +1 and (l +2, l) combine to produce a single output pulse (+4), which is applied across a suitable load 94 such as a load resistor. When the surface wave pulses are in the region of the auxiliary electrodes 72 and 74, only a negligibly small pulse is produced due to the angle between the electrodes 72 and 74 and the surface wave pulses.

There are several advantages obtained by the transducers shown in FIG. 3. There are only two leads connected to the source or the load, therefore, no center ground is required. One of the leads can be grounded; and, hence, the source or the load need not be balanced about the ground potential. There are the same number of electrodes connected to each lead of the transducer; and, therefore, the transducer is well balanced. Also, the surface wave pulse sequences are returnto-zero binary pulses in accordance with proper coding technique. The complementary transducers can also be connected as shown in FIG. 5 wherein the leads to the transducer are much simplified. The result of the operation of FIG. 5 is the same as that of FIG. 3 by the nature of the complementary series, that is, a pair of complementary series is still complementary when one sequence of the pair changes sign.

Another embodiment of the invention is shown in FIG. 6. In FIG. 6, the output transducer consists of a cascaded number of the previously described transducers and is designed to perform a binary sequence pattern recognition. The particular embodiment can be used to recognize a three-digit Barker code sequence. When the input sequence matches the output transducer sections, the output electrical signal is maximum. The function of the angled electrodes is the same as in FIGS. 3 and 5.

The acoustic pulse sequences produced by the input transducer 100 are depicted in FIG. 6 and the resultant electrical output signal from output transducer 102 is also shown. The sections of the transducers can be increased or changed in polarity to recognize any length of binary sequence for any type of code used in information processing.

In still another embodiment of the present invention, only one auxiliary electrode may be employed in place of the pair of auxiliary electrodes. For example, in FIG. 3 either auxiliary electrode 46 or 48 may be eliminated. In this embodiment it may be possible that the undesired pulse will reach the detector transducer, depending on the distance between the generator transducer and the detector transducer. However, the undesired pulse will have a wavefront direction different from the otherpulses, that is, it will not be parallel to the wavefronts of the pulses desired to be detected. Thus, any signal produced by the undesired pulse at the detector transducer will be negligibly small.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An interdigital transducer device for processing surface wave pulse trains comprising a first interdigital transducer structure including first and second parallel leads,

a first plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said first lead;

a second plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said second lead;

a first plurality of linear auxiliary electrodes located in parallel between said first and second parallel leads and disposed at an oblique angle to said first and second parallel leads,

a second interdigital transducer structure including third and fourth parallel leads located adjacent and parallel to said first and second parallel leads,

a third plurality of linear main electrodes located between said third and fourth parallel leads and connected perpendicularly to said fourth lead;

and a second plurality of linear auxiliary electrodes located in parallel between said third and fourth parallel leads and disposed at an oblique angle to said third and fourth parallel leads.

2. An interdigital transducer device according to claim 1 further including means for connecting said first and third leads together,

means for connecting said second and fourth leads together;

a substrate for supporting said first and second interdigital transducer structures, said substrate being composed of material capable of propagating acoustic surface waves;

and wherein said first and second interdigital transducer structures are responsive to an input electrical said for propagating a first train of acoustic surface wave pulses on said substrate from said first transducer structure and a second train of acoustic surface wave pulses on said substrate from said second transducer structure;

said first and second pulse trains propagating in parallel in a given direction.

3. An interdigital transducer device according to claim 2 wherein said main electrodes propagate pulses in a first direction and said auxiliary electrodes propagate pulses in a second direction different from said first direction.

4. An interdigital transducer device according to claim 3 further including a third interdigital transducer structure identical to said first transducer structure and a fourth transducer structure identical to said second transducer structure, said third and fourth transducer structure being located adjacent to each other on said substrate in the path of said first and second pulse trains respectively,

and said third and fourth transducer structures being responsive to said acoustic pulses propagated by saild main electrodes of said first and second transducer structures respectively for producing a related electrical signal.

5. An interdigital transducer device for processing surface wave pulse trains comprising a first interdigital transducer structure including first and second parallel leads,

a first plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said first lead;

a second plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said second lead;

a first plurality of linear auxiliary electrodes located in parallel between said first and second parallel leads and disposed at an oblique angle to said first and second parallel leads,

a second interdigital transducer structure including a third lead parallel and adjacent to said second lead,

a third plurality of linear main electrodes located between said second and third parallel leads and connected perpendicularly to said second lead;

a fourth plurality of linear main electrodes located between said second and third parallel leads and connected perpendicularly to said third lead;

and a second plurality of linear auxiliary electrodes located in parallel between said second and third parallel leads an disposed at an oblique angle to said second and third parallel leads.

6. An interdigital transducer device according to claim 5 further including a substrate for supporting said first and second interdigital transducer structures, said substrate being composed of material capable of propagating acoustic surface waves,

and wherein said first and second interdigital transducer structures are responsive to an input electrical signal for propagating a first train of acoustic surface waves on said substrate from said first transducer structure and a second train of acoustic surface waves from said second transducer structure,

said first and second pulse trains propagating in parallel in a given direction.

7. An interdigital transducer device according to claim 6 wherein said main electrodes propagate pulses in a first direction and said auxiliary electrodes propagate pulses in a second direction different from said first direction.

8. An interdigital transducer device according to claim 7 further including a third interdigital transducer structure identical to said first transducer structure and a fourth transducer structure identical to said second transducer structure, said third and fourth transducer structure being located adjacent to each other on said substrate in the path of said first and second pulse trains respectively,

and said third and fourth transducer structures being responsive to said acoustic pulses propagated by said main electrodes of said first and second transducer structures respectively for producing a related electrical signal.

II 1 l I I! 

1. An interdigital transducer device for processing surface wave pulse trains comprising a first interdigital transducer structure including first and second parallel leads, a first plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said first lead; a second plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said second lead; a first plurality of linear auxiliary electrodes located in parallel between said first and second parallel leads and disposed at an oblique angle to said first and second parallel leads, a second interdigital transducer structure including third and fourth parallel leads located adjacent and parallel to said first and second parallel leads, a third plurality of linear main electrodes located between said third and fourth parallel leads and connected perpendicularly to said fourth lead; and a second plurality of linear auxiliary electrodes located in parallel between said third and fourth parallel leads and disposed at an oblique angle to said third and fourth parallel leads.
 2. An interdigital transducer device according to claim 1 further including means for connecting said first and third leads together, means for connecting said second and fourth leads together; a substrate for supporting said first and second interdigital transducer structures, said substrate being composed of material capable of propagating acoustic surface waves; and wherein said first and second interdigital transDucer structures are responsive to an input electrical said for propagating a first train of acoustic surface wave pulses on said substrate from said first transducer structure and a second train of acoustic surface wave pulses on said substrate from said second transducer structure; said first and second pulse trains propagating in parallel in a given direction.
 3. An interdigital transducer device according to claim 2 wherein said main electrodes propagate pulses in a first direction and said auxiliary electrodes propagate pulses in a second direction different from said first direction.
 4. An interdigital transducer device according to claim 3 further including a third interdigital transducer structure identical to said first transducer structure and a fourth transducer structure identical to said second transducer structure, said third and fourth transducer structure being located adjacent to each other on said substrate in the path of said first and second pulse trains respectively, and said third and fourth transducer structures being responsive to said acoustic pulses propagated by sai-d main electrodes of said first and second transducer structures respectively for producing a related electrical signal.
 5. An interdigital transducer device for processing surface wave pulse trains comprising a first interdigital transducer structure including first and second parallel leads, a first plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said first lead; a second plurality of linear main electrodes located between said first and second parallel leads and connected perpendicularly to said second lead; a first plurality of linear auxiliary electrodes located in parallel between said first and second parallel leads and disposed at an oblique angle to said first and second parallel leads, a second interdigital transducer structure including a third lead parallel and adjacent to said second lead, a third plurality of linear main electrodes located between said second and third parallel leads and connected perpendicularly to said second lead; a fourth plurality of linear main electrodes located between said second and third parallel leads and connected perpendicularly to said third lead; and a second plurality of linear auxiliary electrodes located in parallel between said second and third parallel leads an disposed at an oblique angle to said second and third parallel leads.
 6. An interdigital transducer device according to claim 5 further including a substrate for supporting said first and second interdigital transducer structures, said substrate being composed of material capable of propagating acoustic surface waves, and wherein said first and second interdigital transducer structures are responsive to an input electrical signal for propagating a first train of acoustic surface waves on said substrate from said first transducer structure and a second train of acoustic surface waves from said second transducer structure, said first and second pulse trains propagating in parallel in a given direction.
 7. An interdigital transducer device according to claim 6 wherein said main electrodes propagate pulses in a first direction and said auxiliary electrodes propagate pulses in a second direction different from said first direction.
 8. An interdigital transducer device according to claim 7 further including a third interdigital transducer structure identical to said first transducer structure and a fourth transducer structure identical to said second transducer structure, said third and fourth transducer structure being located adjacent to each other on said substrate in the path of said first and second pulse trains respectively, and said third and fourth transducer structures being responsive to said acoustic pulses propagated by said main electrodes of said first and second transducer structures respectively for producing a related Electrical signal. 